Preface ......................................................... v
About the Editors ............................................. xix
List of Contributors .......................................... xxi
Contents of Volumes in This Set ............................. xxiii
CHAPTER 1. Self-Assembled Germanium Quantum Dots on Silicon
and Their Optoelectronic Devices
I.L.Liu, S.Tong, K.L.Wang
1. Introduction ................................................ 1
2. Structural Properties of Germanium (Ge) Quantum Dots ........ 2
2.1. Single-Layered Ge Quantum Dots on Planar Si ........... 2
2.2. Ge Quantum Dot Superlattice Growth .................... 9
3. Optical Properties of Ge Quantum Dots ...................... 14
3.1. Interband Properties: Photoluminescence Studies ...... 14
3.2. Intersubband Properties .............................. 20
4. Ge quantum dot optoelectronic devices ...................... 22
4.1. Ge Quantum Dot Light Emitting Diodes ................. 22
4.2. Near-Infrared p-i-n Ge Quantum Dot
Photodetectors Operating at 1.31 - 1.55 μm ........... 24
4.3. Mid-Infrared Ge Quantum Dot Photodetectors
Operating at 3 — 5 + μm .............................. 26
5. Summary .................................................... 29
References ................................................. 29
CHAPTER 2. Germanium Self-Assembled Quantum Dots on Silicon:
Growth, Electronic Transport, Optical Phenomena,
and Devices
A.I. Yakimov, A.V. Dvurechenskii, A.I. Nikiforov
1. Introduction ............................................... 34
2. Strain-Driven Quantum Dot Self-Assembly .................... 34
2.1. Basic Concepts ....................................... 35
2.2. Growth of Germanium (Ge) Self-Assembled
Quantum Dots on Si(100) Surface ...................... 36
2.3. Self-Assembling ...................................... 37
2.4. Size and Density of Self-Assembled Quantum Dots ...... 38
2.5. In Situ Reflection High Energy Electron
Diffraction Control of Quantum Dot Growth ............ 39
3. Theoretical Consideration of Electronic Structure .......... 41
3.1. Spatial Distribution of Elastic Strains .............. 41
3.2. Hole Energy Spectrum ................................. 44
3.3. Wave Functions and g-Factor of Holes in
Ge/Si Quantum Dots ................................... 46
3.4. Electronic Configuration of Excitons and
Excitonic Complexes .................................. 58
4. Single-Electron Effects .................................... 60
4.1. Electron Tunneling Spectroscopy ...................... 60
4.2. Capacitance Tunneling Spectroscopy ................... 62
4.3. Tunneling Currents in Schottky Diodes ................ 63
5. Hole Transport and Long-Range Coulomb Interaction .......... 64
5.1. Field Effect in Array of Charge-Tunable Dots ......... 66
5.2. Crossover from Efros-Shklovskii to Mott
Variable-Range Hopping ............................... 70
5.3. Universal Prefactor in Unscreened Regime of
Variable-Range Hopping ............................... 74
6. Optical Properties ......................................... 76
6.1. Spatially Indirect Excitons .......................... 76
6.2. Stark Effect in Ge/SiCySi Quantum Dots ............... 81
6.3. Negative Interband Photoconductivity ................. 85
6.4. Depolarization Shift of the Interlevel Resonance ..... 86
7. Applications ............................................... 88
7.1. Quantum-Dot Metal-Oxide Semiconductor
Field-Effect Transistor .............................. 88
7.2. Ge/Si Self-Assembled Quantum Dots Photodetectors
for Near- and Midinfrared Operation .................. 91
8. Concluding Remarks ......................................... 98
References ................................................. 98
CHAPTER 3. The Size Control and Patterning of Nanocrystalline
Silicon Quantum Dots
Kunji Chen, Xinfan Huang
1. Introduction .............................................. 104
2. The Mechanism and Experiments on Constrained
Growth of Uniform nc-Si Grains ............................ 105
2.1. General Remarks ..................................... 105
2.2. The Model of Constrained Growth ..................... 106
2.3. Experiments and Results ............................. 109
3. Laser Interference-Induced Crystallization and
Formation of Patterned nc-Si Structures ................... 113
3.1. The Intensity Distribution of Laser
Interference Produced by a Phase-Shift Grating ...... 113
3.2. Experimental Setup and Characterization of
Phase-Shift Grating ................................. 117
3.3. Formation of Regularly Patterned One
-Dimensional/Two-Dimensional nc-Si Dots Array ....... 118
3.4. Crystallization Mechanism and Self-Organized
Growth of nc-Si Dots ................................ 120
4. Nanocrystalline Silicon (nc-Si) Superlattices ............. 122
4.1. The Realization of nc-Si Superlattice ............... 122
4.2. Three-Dimensional-Ordered nc-Si Structures .......... 125
4.3. The Effect of Posttreatments on Crystallization
in a-Si:H/a-SiNx:H Superlattices .................... 126
5. Light Emission from nc-Si Films ........................... 131
5.1. Visible Photoluminescence from nc-Si/SiNx
Multilayers ......................................... 131
5.2. Visible and Stable Electroluminescence from
nc-Si/SiNx Multilayers .............................. 133
5.3. Comparison of Light Emission between
Si/SiNx and Si/Si02 Multilayers ..................... 136
6. Electronic Transport Properties in nc-Si Quantum Dots ..... 140
6.1. Conductance Characteristics of Si02/nc-Si QDs /Si02
Double-Barrier Diode ................................ 140
6.2. Size-Dependent Resonant Tunneling and Storing
of Electrons in nc-Si QDs Floating Gate
Structures .......................................... 143
References ................................................ 147
CHAPTER 4. Epitaxial Growth of Semiconductor Self-Assembled
Quantum Dots
H.J. Kim, Z.M. Zhao, B.Shi, J.Liu, Y.H. Xie
1. Introduction .............................................. 149
2. Quantum Dot Based Device Applications ..................... 151
3. Three Growth Modes ........................................ 156
4. Ge Quantum Dot on Si ...................................... 157
4.1. Pyramid to Dome Transition ........................ 157
5. InAs Quantum Dots on GaAs ................................. 174
5.1. Growth Parameters that Strongly Affect
Dot Formation ....................................... 174
5.2. Optical Properties for Optoelectronic
Applications ........................................ 179
5.3. Strain and Dislocations in Quantum Dots ............. 183
5.4. Summary ............................................. 185
6. Other Group Quantum Dots .................................. 185
6.1. Self-Organized GaN Quantum Dots on A1N .............. 185
6.2. Self-Assembled PbSe Quantum Dots on PbTe(lll)
Under Tensile Strain ................................ 187
7. InGaAs Quantum Dots on Si ................................. 188
7.1. Introduction ........................................ 188
7.2. III-V Quantum Dots on IV Substrates ................. 190
7.3. Summary ............................................. 197
8. Conclusion ................................................ 197
References ................................................ 199
CHAPTER 5. Optical and Electrical Transport Properties of Silicon
Nanodots Embedded in Silicon-Rich Silicon Nitrides
Huey-liang Hwang, Zingway Pei, His-lien Hsiao
1. Introduction .............................................. 206
1.1. Electroluminescence ................................. 207
1.2. Resonant Tunneling Diode ............................ 207
1.3. Nanoflash Memory .................................... 208
2. Material Growth and Film Compositions ..................... 208
2.1. Growth of Si-Rich Silicon Nitride Films ............. 208
2.2. Thin Film Characterization .......................... 210
2.3. Summary ............................................. 213
3. Optical Characteristics ................................... 213
3.1. Photoluminescence ................................... 213
3.2. Electroluminescence ................................. 219
3.3. Summary ............................................. 224
4. Observation of Si nanodots ................................ 225
4.1. X-Ray Photoemission Spectroscopy .................... 225
4.2. High-Resolution Transmission Electron Microscopy .... 227
4.3. Summary ............................................. 228
5. Electrical Transport Through Si Nanodots .................. 229
5.1. Mechanisms of Electrical Transport in
Dielectric Film ..................................... 229
5.2. Device Structure .................................... 234
5.3. Transport Characteristics ........................... 236
5.4. Current Transport for Samples with Different
Si Contents ......................................... 240
5.5. Characteristics of Si Nanodot-Related Transport ..... 242
5.6. Summary ............................................. 246
6. Transport Dynamics of Silicon Nanodots .................... 246
6.1. Introduction ........................................ 246
6.2. Experiments ......................................... 246
6.3. Nanodots Capacitance ................................ 247
6.4. Capacitance-Voltage Characteristics ................. 248
6.5. Charging of Carriers ................................ 249
6.6. Summary ............................................. 250
7. Energy Levels in Si Nanodots .............................. 251
7.1. Material Parameters ................................. 252
7.2. Barrier Height ...................................... 253
7.3. Relevance of Band Diagram to Transport .............. 257
7.4. Summary ............................................. 259
8. Conclusions ............................................... 259
References ................................................ 261
CHAPTER 6. Modeling of Quantum Dot Self-Assembly
Christian Lang
1. Introduction .............................................. 265
2. Theoretical Models for the Growth of Quantum Dots ......... 267
2.1. Models for the Island Nucleation .................... 268
2.2. Island Growth ....................................... 270
2.3. Self-Limiting Growth ................................ 271
2.4. The Quantum Dot Shape ............................... 272
2.5. Atomistic Modeling .................................. 273
2.6. Models for Buried Quantum Dots ...................... 274
3. Electronic Properties ..................................... 274
4. Atomistic Modeling of the Composition Profile ............. 276
4.1. An Algorithm for the Atomistic Modeling of
the "Equilibrium" Alloying Profile .................. 276
4.2. The Composition Profile of Pyramid Shaped
Quantum Dots ........................................ 281
4.3. Comparison with the Results of Other Studies ........ 284
5. Analyzing the Energetics of an Atomistic Model ............ 287
5.1. Separating the Different Energy Contributions
to the Total Energy ................................. 288
5.2. Application to the Atomistic Models ................. 291
5.3. The Surface Volume Model ............................ 296
5.4. Summary ............................................. 299
6. Conclusions and Future Outlook ............................ 300
References ................................................ 301
CHAPTER 7. Stress Relaxation in Lattice-Mismatched Semiconductor
Overlayers on Patterned Substrates: Atomistic
Simulation Studies
Maxim A.Makeev, Anupam Madhukar
1. Introduction .............................................. 304
2. Heteroepitaxial Overlayers on Infinite Substrates ......... 306
3. Critical Overlayers: Pathways for Stress Relaxation ....... 307
3.1. Elastic Relaxation .................................. 308
3.2. Stress-Induced Instability .......................... 309
3.3. Non-Elastic Relaxation .............................. 310
4. Lattice-Mismatched Overlayers on Nanoscale Mesas:
An Overview ............................................... 312
4.1. InAs/GaAs Systems: Experimental Results ............. 312
4.2. Ge/Si Systems: Experimental Results ................. 314
4.3. Stress Behavior in the Stripe Mesa
Systems: Theory ..................................... 315
5. Simulation Methodology .................................... 316
5.1. Interatomic Potential Scheme for Ge/Si Systems ...... 316
5.2. Interatomic Potential Scheme for InAs/GaAs
Systems ............................................. 317
5.3. Methodology of Atomically Stress Tensor
Calculations ........................................ 318
6. Atomistic Approach to the Problem of Stress Behavior ...... 318
6.1. Ge/Si Square Mesa Systems ........................... 318
6.2. InAs/GaAs Stripe Mesa Systems ....................... 320
7. Fundamental Issues of the Stress Behavior in
Mesa Systems .............................................. 320
7.1. Atomic Displacement Fields in Ge/Si ................. 320
7.2. Non-Linear Effects in the Stress-Strain
Relation ............................................ 323
7.3. Hydrostatic Stress Behavior in Ge/Si Mesa
Systems ............................................. 325
7.4. Energetics of the Ge Overlayer Covered Si
Mesa Systems ........................................ 326
7.5. Stress Behavior in the Lateral Direction ............ 328
8. Stress Behavior in the InAs/GaAs Stripe
Mesa Systems .............................................. 331
9. Notes on the Phenomenon of Preferential Islanding ......... 332
10. Summary and Conclusions ................................... 334
References ................................................ 335
CHAPTER 8. Single and Highly Dense Germanium/Silicon
Nanostructures
Alexander Shklyaev, Masakazu Ichikawa
1. Introduction .............................................. 338
2. Self-Organization of Ge Layers on Si Surfaces
at the Stranski-Krastanov Growth Mode ..................... 339
2.1. Ge on Si(lll) ....................................... 339
2.2. Ge on Si(100) and Si(311) Surfaces .................. 348
2.3. Effect of Surface Anisotropy on Ge Growth ........... 349
3. Formation of Single Nanostructures Using
Instability of Two-Diemensional Ge Layers ................. 351
3.1. Nucleation of Ge Islands Stimulated by
Electron-Beam Irradiation ........................... 351
3.2. Ge Nanostructures Created with the Scanning
Tunneling Microscope Tip ............................ 351
3.3. Ge Islands on Si Windows in Si Oxide Films .......... 357
4. Single Ge/Si Nanostructures Grown from Si2H6 and GeH4 ..... 360
4.1. Si Window Formation in Ultrathin Si02 Films
on Si Substrates .................................... 360
4.2. Selective Growth and Stability of Si
Nanocrystals on Si(001) Windows ..................... 360
4.3. Selective Growth of Ge on Si Windows ................ 362
4.4. Selective Growth of Ge/Si and Si/Ge/Si
Nanoislands ......................................... 362
5. Ge Islands on Oxidized Si Surfaces ........................ 365
5.1. Structure and Density of Ge Islands ................. 365
5.2. Growth Mechanism .................................... 368
6. Morphology of Silicon Layers on Oxidized Si Surfaces ...... 372
6.1. Structure and Density of Ultrasmall
Three-Dimensional Si Islands ........................ 372
6.2. Stability of Three-Dimensional Si
Surface Morphology .................................. 373
6.3. Areal Density of Ultrasmall Si Islands .............. 376
7. Multilayer Structures of Highly Dense Ge Dots ............. 378
7.1. Si Growth on Layers of Ge Dots ...................... 378
7.2. Photoluminescence in Infrared and
Visible Ranges ...................................... 381
8. Conclusion ................................................ 383
References ................................................ 383
CHAPTER 9. Modeling of Electrostatically Gated Vertical
Quantum Dots
J.Adamowski, S.Bednarek, B.Szafran
1. Introduction .............................................. 390
2. Structure of Nanodevices .................................. 392
2.1. Two-Terminal Quantum Dots ........................... 392
2.2. Three-Terminal Quantum Dots ......................... 392
3. Single-Electron Tunneling Spectroscopy .................... 394
3.1. Conditions of Single-Electron Tunneling ............. 395
3.2. Single-Electron Capacitance Spectroscopy ............ 396
3.3. Single-Electron Transport Spectroscopy .............. 397
4. Poisson-Schrodinger Problem ............................... 399
4.1. Electrostatic Fields in QDs ......................... 400
4.2. Boundary Conditions ................................. 403
4.3. Numerical Integration of the Poisson Equation ....... 404
4.4. Hartree-Fock Method ................................. 406
5. Quantum Coulomb Blockade .................................. 406
5.1. Theoretical Description of Single-Electron
Tunneling ........................................... 406
5.2. Induced-Charge Density Distribution ................. 410
6. Modeling of Confinement Potentials ........................ 411
6.1. Three-Dimensional Profile of the
Confinement Potential ............................... 411
6.2. Lateral Confinement ................................. 411
6.3. Parabolic Confinement Potential ..................... 416
7. Effect of External Magnetic Field ......................... 419
8. Correlation Effects ....................................... 423
9. Wigner Molecules .......................................... 426
9.1. Wigner Localization ................................. 426
9.2. Circular Quantum Dots ............................... 427
9.3. Anisotropic Quantum Dots ............................ 433
9.4. Exact Broken-Symmetry Solutions ..................... 433
10. Artificial Molecules ...................................... 436
11. Discussion ................................................ 442
12. Applications .............................................. 446
12.1. Single-Electron Transistor ......................... 446
12.2. Quantum Computation ................................ 446
13. Conclusions .............................................. 448
Glossary .................................................. 448
References ................................................ 449
CHAPTER 10. Carrier Transport and Gap States in Semiconductor
Nanostructures
Diana Nesheva
1. Introduction .............................................. 453
2. Carrier Transport in Semiconductor Superlattices .......... 454
2.1. Perpendicular Transport ............................. 454
2.2. In-Plane Transport and Charge Transfer in SLs ....... 458
2.3. Metastable Phenomena ................................ 460
3. Carrier Transport in Nanocrystalline Layers and
Composite Films ........................................... 463
3.1. Percolation ......................................... 464
3.2. Tunneling ........................................... 472
4. Defect States in Nanoparticles and Ultrathin Layers ....... 478
4.1. Binding Energy of Impurity States ................... 478
4.2. Defect States in Nanosized Semiconductors ........... 479
5. Concluding Remarks ........................................ 492
References ................................................ 492
Index ..................................................... 499
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